JPH1138932A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device capable of suppressing the generation of pseudo contour disturbance with respect to an image display device, which represents different gradations by dividing one frame of image into plural sub-frames and making necessary sub-fields alone selectively emit light in accordance with the gradation of each pixel. SOLUTION: A sub-field candidate calculating section 22 has at least two kinds of combinations of sub-fields to be selected from among plural sub-fields to represent a specified gradation. When two candidates are outputted from the candidate calculating section 22, a sub-field allotment determining section 24 reads pixel values positioned in the surroundings of the pixel which represents the gradation from a memory section 23 and selects the candidate that gives a combination of representation closer to the gradation representation of the stored pixel. Accordingly the difference in gradation representation between neighboring pixels can be suppressed and an image display device which can suppress the generation of pseudo contour disturbance is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image display device.

[0002]

2. Description of the Related Art For example, an image display device such as a plasma display device, unlike a cathode ray tube, cannot arbitrarily change the light emission intensity of each pixel. Therefore, the gray scale is expressed by changing the light emission time in accordance with the gray scale using the integration effect of the human eye.

However, in the case of a plasma display device, light emission is performed simultaneously on a plane basis. That is, it is possible to select whether or not to emit light for each pixel in one light emission, but it is difficult to finely change the light emission time for each pixel.

Therefore, for example, “Journal of the Institute of Image Information and Television Engineers”, Vol. 51, No. 4 (1997), p. 46
As described in “Moving Picture Quality and Signal Processing of PDP” on pages 4 to 469, in such a display device, the following method is used to display different gradations for each pixel. Have been.

That is, as shown in FIG. 10, one frame image is divided into a plurality of subfields (in FIG. 10, eight subfield numbers 0 to 7). A predetermined length of light emission time is assigned to each subfield (T, 2T,..., 64T, 128).
T). Emission / non-emission of each subfield can be selected for each pixel of an image.

[0006] By selectively emitting light only in necessary subfields in accordance with the gradation of each pixel, display of a different gradation for each pixel is realized.

[0007]

However, when the above-described gradation display by subfield division is performed, there is no problem when displaying a still image, but when displaying a moving image, it is called a pseudo contour. Interference occurs.

This will be described below with reference to FIG. FIG. 11A shows a still image, and FIGS. 11B and 11C show a moving image. In FIG. 11, for simplicity of description, there are four subfields, and the upper part of the figure is L
On the SB side, the lower side is the MSB side. FIG.
In each of (a), (b), and (c), display examples of gray scales of two pixels adjacent to each other are shown. Then, adjacent areas in the figure have slightly different gradations.

In the case of FIG. 11A, that is, in the case of a still image, since the gradation of the adjacent area is slightly different, the light emission / non-light emission on the MSB side changes, and the pattern of the light emitting subfield is changed. Has changed significantly. However, the frame image perceived as the sum of each subfield is a correct image corresponding to the gradation.

On the other hand, in the case of FIGS. 11B and 11C,
That is, in the case of a moving image, since the image is moving at an appropriate speed, the human eyes have a property of trying to follow the moving image.
As a result, the images of the subfields having slightly different display times are perceived with a slight shift from the original position, and the frame images perceived as the sum of the respective subfields are shown in FIGS. ) Causes extra erroneous image information.

That is, in the case of FIG. 11B, the light emission amount at the boundary between adjacent pixels is larger than that in the case of an accurate image. In the case of FIG. 11C, the light emission amount at the boundary between adjacent pixels is smaller than that in the case of an accurate image. This is a false contour obstruction.

As described above, when gradation display is performed by sub-field division, there is a problem that pseudo contour interference may occur at the time of displaying a moving image, resulting in a significant decrease in image quality.

An object of the present invention is to divide an image of one frame into a plurality of sub-frames, selectively emit light only in necessary sub-fields according to the gradation of each pixel, and generate different gradations for each pixel. An object of the present invention is to realize an image display device capable of suppressing occurrence of false contour disturbance in an image display device to be expressed.

[0014]

[Means for Solving the Problems]

(1) In order to achieve the above object, the present invention is configured as follows. That is, an image of one frame is divided into a plurality of subfields having different display times, and display and non-display in each subfield can be selected in pixel units.
In an image display device that expresses a gray scale by summing the light emission amount that is the product of the luminance and the light emission time in each subfield in a plurality of subfields, for a specific gray scale, to express it, When at least two types of combinations of which of the plurality of subfields are to be displayed are provided, and when the specific gradation is to be expressed, one of the two or more types of combinations is selected.
And selecting means for selecting one.

(2) Preferably, in the above (1),
The selection unit refers to a gradation value of one or a plurality of pixels existing around a pixel for which the specific gradation is to be displayed, and according to a function indicating the gradation of the referenced pixel. One of two or more combinations is selected.

(3) Preferably, in the above (1), the selecting means randomly selects one of the two or more kinds of combinations.

(4) One frame image is divided into a plurality of subfields having different display times, and display or non-display in each subfield can be selected in pixel units. In an image display device that expresses a gray scale by summing the light emission amount, which is the product of the above, in a plurality of subfields, pixels belonging to a specific range of the gray scale are replaced with other gray scales belonging to the specific range. The image processing apparatus includes a gradation conversion unit that independently converts a value into a value for each pixel.

(5) Preferably, in the above (4),
The gradation conversion unit refers to a gradation value of one or a plurality of pixels existing around a pixel whose gradation is to be converted, and converts the gradation value according to a function indicating the gradation of the referenced pixel. Determine the tone value.

(6) Preferably, in (4), the gradation conversion means randomly selects and determines the converted gradation value from the specified range of gradation values.

By adopting the configuration shown in the above (1) to (6), it is possible to suppress a difference in gradation expression between adjacent pixels, and to suppress the occurrence of pseudo contour disturbance. Can be realized.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a main part of an image display apparatus according to a first embodiment of the present invention, and FIG. 2 is a schematic diagram of the entire image display apparatus according to the first embodiment. It is a block diagram. Note that the first embodiment is an example in which the present invention is applied to a plasma display device.

In FIG. 2, an image signal input to the plasma display apparatus 1 is divided into sub-fields by a sub-field processing unit 2 for each frame. The signal that has been subfielded by the subfielding processing unit 2 is input to the drive circuit 3, and the drive circuit 3 causes the display panel 4 to emit light for each subfield.

FIG. 1 is an internal block diagram of the subfield processing unit 2. The input image signal is stored in the memory 23
And the subfield candidate calculation unit 22
Supplied to Then, the subfield candidate calculation unit 22
In consideration of the weight for each subfield,
Subfield division is performed.

In general, by appropriately selecting the ratio of the light emission time to be allocated to each subfield in advance, the method of allocating a subfield for expressing a specific gray level of an input image signal is expressed. It can be more than the street.

For example, as shown in FIG. 3, it is assumed that an image of one frame is represented by eight subfields (SF0 to SF7). Here, as shown in FIG. 3A, the ratio of the light emission time of each subfield is 1, 2, 4,.
If the power is a power of 2 such as 8,..., 128, the set of subfields used to represent a certain value is determined uniquely.

However, as shown in FIG. 3B, the ratio of the light emission time of each subfield is (1, 2, 4, 7, 1).
4, 28, 56, 112), for example, to express a value of 7, the subfields SF0, SF1,.
There are two methods, a method of selecting SF2 and a method of selecting only subfield SF3.

Similarly, there are two combinations of subfields representing values such as 14, 28, 56, and 112. That is, for example, in the case of 14, the subfields (SF0, SF1, SF2, SF
3) and subfield SF14. Also,
28, the subfields (SF0, SF1, SF
2, SF3, SF4) and subfield SF5.

In the first embodiment of the present invention, the weights shown in FIG. 3B are used.

In FIG. 1, when there is only one kind of subfield assignment method for expressing a specific gradation of an input image signal, the subfield candidate calculation unit 22 Is output. When two types exist as described above, a combination of both is output as candidate 1 and candidate 2. The memory unit 23 stores the pixel values input to the subfield processing unit 2.

Sub-field allocation determining section (selection means) 2
No. 4 outputs the subfield as it is when the method of allocating the subfield output from the subfield candidate calculation unit 22 is one. When there are a plurality of (two types) of subfield allocation methods output from the subfield candidate calculation unit 22, one of them is selected and output.
The selection is performed as follows with reference to the values of the peripheral pixels stored in the memory unit 23.

That is, as shown in FIG. 4, there are two types of expression methods ((SF0, SF1, SF2), (SF3)) of the value 7 as shown in FIGS. 4 (a) and 4 (b). According to the information read from the memory unit 23, the value of the adjacent area is 6
In this case, even if pseudo contour interference in a moving image occurs, it is less noticeable in the subfield allocation method (a) (SF1 and SF).
2 is common to 6 and 7). If the value of the adjacent area is 8, the interference is less noticeable in (b) where SF3 is common.

In consideration of the above, the sub-field assignment determining unit 24 selects an assignment method that is less likely to cause pseudo contour interference from the values of the peripheral pixels. For example, a display method is selected in which there are many common subfields with the value of the largest number of pixels among the plurality of neighboring pixels of the pixel to be displayed (the values of the plurality of neighboring pixels are, for example, 6, 6, 6, 6). ,
If it is 6, 8, 8, or 8, a display method having many display sub-fields in common with the display sub-field of 6 is selected).

Of the pixels surrounding the pixel to be displayed,
Regarding which pixel value is to be adopted, a method other than the method described above can be considered. For example, of the peripheral pixels, pixels adjacent to the pixel to be displayed on the left and right may be weighted, compared with other peripheral pixels, and any one of them may be adopted. Which of the peripheral pixels is adopted can be expressed as a predetermined function (a function that adopts the most of the peripheral pixels described above, a function that is employed with weight, and the like), According to the predetermined function, the value of the peripheral pixels is adopted, and the display method whose expression is closer to the adopted value is selected.

As described above, according to the first embodiment of the present invention, in order to express a predetermined gradation, at least two types of combinations of which subfields of a plurality of subfields are to be displayed are provided. Have more. Then, when expressing a predetermined gradation, the value of a pixel located around the pixel expressing the gradation is stored in the memory unit 23, and the stored gradation of the pixel is determined based on the closer combination. An expression is selected by the sub-field assignment determining unit 24.

Therefore, it is possible to suppress a difference in gradation expression between adjacent pixels, and to realize an image display device capable of suppressing occurrence of false contour disturbance. That is, in the first embodiment, it is possible to realize a plasma display device in which pseudo contour interference in a moving image is reduced.

Next, a second embodiment of the present invention will be described. The difference of the second embodiment from the first embodiment is the subfielding processing section 2. Other parts are the same as in the first embodiment, and a description thereof will be omitted. Note that the second embodiment is also an example in which the present invention is applied to a plasma display device.

FIG. 5 is an internal block diagram of the subfield processing unit 2 in the image display device according to the second embodiment of the present invention. In FIG. 5, the subfield candidate calculation unit 22 is a subfield candidate calculation unit 2 shown in FIG.
The same processing as in step 2 is performed. That is, if there is only one type of subfield assignment for expressing a specific gradation of an input image signal, it is output. When two types exist as described above, a combination of both types is output.

The random number generator 25 generates a random number from "1" to "the maximum value of the number of combinations of subfields output from the subfield candidate calculator 22". That is, in the case of the second embodiment, the random number generation unit 25 generates a value of either 1 or 2 as a random number.

The subfield allocation determining unit 24 outputs the subfield output from the subfield candidate calculation unit 22 as it is when there is only one type of subfield allocation. When there are a plurality of (two) ways of assigning subfields output from the subfield candidate calculation unit 22, one is selected and output. The selection is determined by the random number output from the random number generator 25.

That is, when the random number generated by the random number generator 25 is 1, candidate 1 is selected from the subfield assignments output from the subfield candidate calculator 22. The random number generated by the random number generation unit 25 is 2
In the case of (2), candidate 2 is selected from the subfield assignments output from the subfield candidate calculation unit 22.

As described above, by randomly selecting the method of assigning subfields using random numbers, that is, at random, even if false contour interference occurs, it is dispersed and becomes less noticeable.

As described above, according to the second embodiment of the present invention, similarly to the first embodiment, it is possible to suppress a difference in gradation expression between adjacent pixels, and to suppress false contour interference. It is possible to realize a plasma display device which is an image display device whose generation can be suppressed.

Next, a third embodiment of the present invention will be described. The difference between the third embodiment and the first embodiment is the subfielding processing unit 2. Other parts are the same as in the first embodiment, and a description thereof will be omitted. Note that the third embodiment is also an example in which the present invention is applied to a plasma display device.

FIG. 6 is an internal block diagram of the subfield processing section 2 in the image display device according to the third embodiment of the present invention. In FIG. 6, the memory unit 23 stores the pixel value input to the subfield processing unit 2.

The gradation converter 26 performs the following conversion on the input image signal. That is, if the tone value of the input image signal does not belong to a predetermined specific range, the value is output as it is, and if it belongs to the specific range, the tone value is changed to another tone value within the range. Convert.

FIG. 7 is a graph showing the relationship between the input value and the output value in the gradation converter 26. For example, assuming that the input gradation value is a value belonging to the range from 126 to 129, one of the values in the range from 126 to 129 is selected and output. The method of selecting the value will be described below.

If the ratio of the light emission time of each subfield is set to be a power of 2, the gradation values from 126 to 129 can be expressed by the subfield as shown in FIG. In FIG. 8, 126 and 127 and 12
8 and 129 are different from each other in whether or not to use the MSB. This is a portion where the expression pattern of the subfield changes significantly. That is, it is a portion where a false contour easily occurs when the values interfere with each other in the moving image.

Therefore, assuming that the value of the adjacent area is 126 or 127 using the information read from the memory unit 23, the converted value is also set to 126 or 127, thereby making the false contour disturbance less noticeable. be able to. It should be noted that which of 126 and 127 is to be selected is to select the one closer to the original input value.

Similarly, assuming that the value of the adjacent area is 128 or 129, the converted contour value is also set to 128 or 129, so that the false contour disturbance can be made inconspicuous. It should be noted that which of 128 and 129 is to be selected is to select the one closer to the original input value.

The output of the tone converter 26 is subjected to subfield division in the subfield calculator 27 in accordance with the weight for each subfield.

As described above, according to the third embodiment of the present invention, when the gradation value of the input image signal does not belong to a predetermined range, the gradation value is output as it is, and If the value belongs to a specific range, the information read from the memory unit is used. If the value of the adjacent area greatly changes in the expression pattern of the subfield, the pixel to be displayed is set to the value of the adjacent area. It is configured to convert to

Therefore, similarly to the first embodiment, it is possible to suppress a difference in gradation expression between adjacent pixels.
A plasma display device, which is an image display device capable of suppressing the occurrence of false contour interference, can be realized.

Next, a fourth embodiment of the present invention will be described. What differs from the third example of the fourth embodiment is the part of the subfielding processing unit 2. The other parts are the same as in the third embodiment, and a description thereof will be omitted. The fourth embodiment is also an example in which the present invention is applied to a plasma display device.

FIG. 9 is an internal block diagram of the subfield processing unit 2 in the image display device according to the fourth embodiment of the present invention. In FIG. 9, the gradation conversion unit 26 performs the following conversion on the input image signal. That is, if the gradation value of the input image signal does not belong to a predetermined specific range, the value is output as it is, and if it belongs to the specific range, another gradation value within that range is used. Convert to

As shown in the graph of FIG. 7, for example, if the input value is a value belonging to the range from 126 to 129, the output is selected from the values in the range from 126 to 129. Output. The value is selected at random using a random number generated by the random number generation unit 25.

The subfield calculator 27 is the same as that of the third embodiment, and a description thereof will be omitted.

As described above, according to the fourth embodiment of the present invention, similarly to the third embodiment, it is possible to suppress the difference in the gradation expression between adjacent pixels, and to suppress pseudo contour interference. It is possible to realize a plasma display device which is an image display device whose generation can be suppressed.

As another example of the above embodiment, the first
An example in which the third embodiment or the fourth embodiment is combined with the third embodiment or the fourth embodiment can be considered. In this case, when the gradation value of the input image signal does not belong to a predetermined range, the signal value is subjected to the signal processing of the first embodiment or the second embodiment. If the gradation value of the input image signal belongs to a predetermined specific range, the third embodiment or the fourth embodiment
The signal processing of the embodiment is performed.

In each of the above embodiments, the ratio of the light emission time for each subfield and the number of subfields used as examples are not limited thereto.

Further, the range of values for performing gradation conversion in the third and fourth embodiments is not limited to the values exemplified in the text.

Further, the above-described example is an example in which the present invention is applied to a plasma display device. However, the present invention is not limited to a plasma display device, and an image of one frame is divided into a plurality of subfields. The present invention can be applied to other devices as long as the image display device expresses a gradation by summing the light emission amount, which is the product of the luminance and the light emission time in each subfield, in a plurality of subfields.

[0062]

The present invention is configured as described above, and has the following effects. In order to express a predetermined gradation in an image display device that divides an image of one frame into a plurality of subframes and selectively emits only necessary subfields according to the gradation of each pixel to express different gradations Has at least two types of combinations of which subfields of a plurality of subfields are to be displayed. Then, when expressing a predetermined gradation,
The gradation expression of a pixel located around the pixel expressing the gradation and the expression based on the closer combination are selected.

Accordingly, it is possible to suppress a difference in gradation expression between adjacent pixels, and to realize an image display device capable of suppressing occurrence of false contour interference.

Even if two types of combinations of subfields are selected at random, it is possible to realize an image display device capable of suppressing the occurrence of false contour interference.

When the gradation value of the input image signal does not belong to a predetermined specific range, the value is output as it is, and when it belongs to the specific range, the information read from the memory unit is read. If the value of an adjacent area greatly changes in the expression pattern of a subfield, even if the pixel to be displayed is converted to the value of the adjacent area, the occurrence of false contour interference may occur. It is possible to realize an image display device capable of suppressing the occurrence of an image.

If the gradation value of the input image signal does not belong to a predetermined range, the gradation value is output as it is. If the gradation value of the input image signal belongs to the specified range, the gradation value is randomly selected. However, even if the configuration is such that a value belonging to is selected, it is possible to realize an image display device capable of suppressing occurrence of false contour interference.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an image display device according to a first embodiment of the present invention.

FIG. 2 is an overall schematic configuration diagram of the image display device according to the first embodiment.

FIG. 3 is a diagram illustrating an example of a subfield division method.

FIG. 4 is a diagram illustrating selection of a gradation level expression method.

FIG. 5 is a main part configuration diagram of an image display device according to a second embodiment of the present invention.

FIG. 6 is a main part configuration diagram of an image display device according to a third embodiment of the present invention.

FIG. 7 is a graph showing an input / output relationship of a gradation conversion unit.

FIG. 8 is a diagram illustrating selection of a gradation level expression method.

FIG. 9 is a main part configuration diagram of an image display device according to a fourth embodiment of the present invention.

FIG. 10 is a diagram illustrating division of a subfield.

FIG. 11 is a diagram illustrating pseudo contour interference.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma display apparatus 2 Sub-field processing part 3 Drive circuit 4 Display panel 22 Sub-field candidate calculation part 23 Memory part 24 Sub-field allocation determination part 25 Random number generation part 26 Gradation conversion part 27 Sub-field calculation part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideo Arai 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Multimedia System Development Division, Hitachi, Ltd. 292 Hitachi Electronics Co., Ltd. Home Appliances & Information Media Business Headquarters (72) Inventor Keizo Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi Electronics Home Appliances & Information Media Business Headquarters (72) Inventor Akihiko Kogami 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref.Hitachi, Ltd.Household Electronics and Information Media Business Headquarters (72) Inventor Kazutaka Naka 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. In headquarters

Claims (6)

[Claims] 1. An image of one frame is divided into a plurality of subfields having different display times, and display or non-display in each subfield can be selected on a pixel basis, and a product of luminance and light emission time in each subfield. In an image display device that expresses a gray scale by summing the light emission amount of a plurality of sub-fields in a plurality of sub-fields. Image display, wherein at least two types of combinations are displayed, and in the case of expressing the specific gradation, there is provided a selecting means for selecting one of the two or more types of combinations. Display device. 2. The image display device according to claim 1, wherein said selecting means refers to a gradation value of one or a plurality of pixels present around a pixel for displaying said specific gradation. An image display apparatus, wherein one of the above two or more combinations is selected according to a function indicating the gradation of a pixel to be referred to. 3. The image display device according to claim 1, wherein said selecting means selects one of said two or more combinations at random. 4. An image of one frame is divided into a plurality of subfields having different display times, and display or non-display in each subfield can be selected on a pixel basis, and a product of luminance and light emission time in each subfield. In an image display device that expresses a gray scale by summing the light emission amounts of a plurality of sub-fields, pixels belonging to a specific range of gray scales are converted to other gray scale values belonging to the specific range. An image display device comprising: a gradation conversion unit that performs conversion independently for each image. 5. The image display device according to claim 4, wherein said gradation conversion means refers to a gradation value of one or a plurality of pixels present around a pixel whose gradation is to be converted, An image display device, wherein a gradation value after conversion is determined according to a function indicating a gradation of a pixel to be referred to. 6. The image display device according to claim 4, wherein said gradation conversion means randomly selects and determines a converted gradation value from said specific range of gradations. Image display device.